I am currently looking to buy an alternator for my 1988 Z31.

 

If nobody has a good OEM for cheap here, the aftermarket stuff isn't bad. Bring your old one in when you order so you can see that they match by the fotos and you have a good fit. All are rebuilt jobs from some factory. Beck-Arnley for maybe $130, Bosch for up to $150. Other stuff for around $100. As long as the replacement could put out 14v on the highway I was happy. There is a core charge so bring your old one back again when your order comes in and avoid that charge. Up to $50 in some places. They warranty their stuff - but you get to do the labor twice if they sell you a dog. Only happened once. I took the cheapest one that time. Basically it's a new rebuild of a used alt. If you want to know how much you save, check your Nissan dealer for the OEM one. (ouch)

Also check out car-part.com. Choose USA only and sort the parts by 'distance.' This will show you the recyclers in your area and what they may have for Z31s. Enter a common part for a common car to find all of the recyclers in your area. I'm sure somebody will have a used OEM Z31 alternator if you want to go that route.